Segmented viscoelastic bushing for rotating electrical machines bearing

ABSTRACT

The present invention discloses a device designed with the purpose of absorbing radial and axial expansion variations during the rotating electrical machine operation. The bushing is fitted between the bearing and the wheel hub in order to absorb impacts, but allowing in a controlled level the axial and radial movement of the bearing resulting from the existing clearance between the bearing and the outer ring of the bearing.

TECHNICAL FIELD

The present invention discloses a segmented viscoelastic device inserted between the wheel hub and the bearing in such a way to eliminate the conventional machining need and additionally reducing noises and vibrations in bearing hubs for motors and generators, which step currently requires high dimensional accuracy.

BACKGROUND OF THE INVENTION

In general, the drawbacks resulting from the frictional resistance to the high-speed of the sliding bearings led to the development of roller bearings. These comprise devices, composed of a pair of steel rings (rails) separated by one or more rows of balls or rollers (rolling bodies), which eliminate the sliding friction. Such balls are kept equidistant to each other through a cage, to distribute forces and maintain the rings concentric; the outer ring is fixed to the wheel hub and the inner ring is attached directly to the axis. The bearings can interact with two types of loads: radial and axial. The radial force is that extending or moving from a central point outwardly and the axial force is that extending or dissipating through the central axis.

The roller bearing housing in the hub cavity requires machining processes of high dimensional accuracy, so the bearing does not move radially inside the cavity. For this reason, the dimensional variation is usually determined by the bearing supplier. However, the conventional processes for obtaining the bearing hub do not ensure the dimensional repeatability required by the system without further accuracy finishing, typically grinding, and the effect of this is the difficulty of assembly or excessive clearance of the bearing in the hub. In this case the outer track of the bearing rotates within the cavity with a high possibility of noises and wear, reducing the product lifetime.

Typically, in a construction of single-phase or three-phase induction motor, with squirrel cage rotor, the air gap value should be sized according to the machine design and a series of combined data. A text, published in 1936, states that “. . . it is necessary (to lower the magnetizing current) using a size of small air gap (but not too small) . . . . The [clearance] must be chosen such that the excitation current and reactance of the machine are in accordance with the desired performance. Reduced gaps can increase motor noise and losses in the tooth face . . . ”

The existing variations in the air gap will depend on the slit dimensions, estator and configuration of the winding. In any case, an air gap variation up to 20% does not result in a significant change in the performance of the locked rotor, fundamental point in motors performance.

In motor applications for areas with fractional commercial ventilation, i.e., with powers lower than 1 cv the radial loads are usually small when proportionally compared to the mechanic resistance of the viscoelastic bearing. In these conditions, the bearing barely touches the seat of the wheel hub in normal application, maintained only by the elastic action of the viscoelastic bushing, which causes the set to operate in an advantageous situation in relation to the noise. Usually, it is desired that the noise is low to this application type, when compared to others conventional applications of rotating electrical machines. In this application, we typically find air gap values in products normally commercialized with values between 0.2 to 0.35 mm.

In particular, applications in rotating electrical machines require certain accuracy care and assembly alignments, due to standard requirements allowing minimal controlled values of durability, noises and vibrations; determining that the wheel hubs of roller bearings are usually built through machining.

DESCRIPTION OF THE STATE OF THE ART

In the state of the art, there are devices aiming to compensate the mistakes between bearings and hub resulting from the thermal expansion between components; for example, in the case of using bearing in aluminum bearing, where it is known that the aluminum expansion is three-times close to the bearing steel, to which tolerance rings or shells are used as intermediate components. In other cases of heavy applications and high temperature, in order to avoid the expansions cause the components latching, non-segmented bushings are used, manufactured from the rubber. In this case, the main drawback relates to the fact of such devices do not meet the concentricity requirement when submitted to radial tensions.

The U.S. Pat. No. 2,886,354 discloses a bushing, under a wavy ring shape which spikes extend axially, so the undesired radial pressure is distributed between the spikes corners, in order to eliminate the possibility of friction, increasing the contact pressure between bearing and wheel hub, being built in a type of “spring” steel by stamping.

The U.S. Pat. No. 3,061,386 of 1958 discloses a tolerance ring manufactured from the metal sheets, comprising projections embossed in half-cylinder shape, similar to the former one, with different shapes and exploring more deeply the wavy shapes control.

The U.S. Pat. No. 3,033,622 discloses a set comprising a bushing for interposition between two pieces as an axis and a bearing, under hexagonal springs shape, absorbing exceeding radial pressures. The drawback associated to this patent is the fact that the same has the requirement to be cloistered through a screwed disc to the wheel hub, increasing severely the manufacturing costs of the mounted system.

The patent GB723399 discloses an elastic device, manufactured from the rubber or silicon rubber, presenting a U-shape or ring shape. The device is found in a compressed state when inserted between a ring and a cavity wall, such that to compensate axial variations.

The U.S. Pat. No. 7,452,135 discloses a bearing support under the shape of a serial set of annular plates stacked in cone shape between the housing wall and the bearing ring outer track. Annular plates can be formed from a single wire, coil, or from a plurality of annular cones stacked in series, whose single purpose is to allow radial dimensional variations with spring effect.

The U.S. Pat. No. 4,699,528 describes a set including an axis and a bearing interposed between the axis and its housing to provide radial support and relative rotation, aiming to absorb radial and axial variations. However, said set comprises a series of combined elements and a specific bearing, mounted in the machine itself holding its operation targeting more severe applications with high temperatures, presenting high complexity and increasing the production costs.

The U.S. Pat. No. 5,611,628 describes a bearing sleeve positioned around a rotation axis, comprising ripples and valleys on its surface, used to compensate radial or axial variations, presented in a preferred embodiment, slits towards the axial flexion.

The U.S. Pat. No. 4,486,055 discloses a compensation device of radial variations, comprising wedges in rim shape. This system consists of a separator ring between the spring and the bearing, with axial pre-tension aiming to dimension the system in such that to allow the increase in the bearing dimensional radial without damage its operation. A drawback of the device is the machining need of the inner diameter of the wheel hub, due to the sliding that must be needed of the separator ring.

The document U.S. Pat. No. 2,926,051 discloses a bearing elastic bushing presenting an inner diameter higher than the outer diameter and an axial pre-tension spring.

The document FR2839396 discloses a ring presenting a profile in L produced from an elastic material to provide damping and presenting an axial dimension corresponding to one and a half times the bearing width, which causes a lot of dimensional disturbances. Particularly in this case the manufacturing dimensional accuracy is identical to a rigid system.

The U.S. Pat. No. 7,223,020 discloses a set of bearing having an outer ring and an inner ring. The outer ring of the bearing is axially fitted in a recess of an inner cylindrical wall. An element radially flexible is located between at least one of the outer rings from bearing and from the recess inner wall, and the inner ring of the bearing and a rotating member that is rotativelly conducted in the set of bearing.

From the above, it is clear that systems for absorbing axial and radial deformations are known in the prior art. However, it is noted that there is not in the current state of the art a device that compensates simultaneously radial and axial dimensional variations generated between the bearing and the cavity wall that houses it, eliminating the need for machining the bearing hub, and associated to a simplified, cost-reduced, productive process, either in obtaining the bearing hub or the radial clearances compensator device proposed herein.

OBJECT OF THE INVENTION

Thus, it is the object of the present invention application overcome the drawbacks found in the prior art, disclosing a segmented viscoelastic material bushing mounted between hub and bearing, eliminating machining steps, so that undesirable axial and radial variations are compensated without damage to the perfect operation of the system.

The present invention discloses a bushing designed with the purpose of absorbing radial and axial expansion variations during the electrical machine operation and the clearances obtained from the high-pressure injection process of the wheel hub without requiring, related to the latter one, any subsequent machining or precision finishing. The bushing is fitted between the bearing and the wheel hub in order to damp impacts, however allowing in a controlled level the radial and axial movement of the bearing resulting from the existing clearance between the bearing and the outer ring of the bearing, limited at 30% of the air gap. Thus, the present invention aims to avoid the set axis/bearing remains loose in the cavity, through the elastic pressure, avoiding turn movements, in which the bearing can rub against the wheel hub causing wear, increase the temperature, undesirable noises and vibrations. This is possible, obtaining the electrical machine bearing through the high-pressure casting process, that will provide the suitable accuracy for concentricity and finishing for the proposed application.

BRIEF DESCRIPTION OF FIGURES

FIG. 1 illustrates a rear view of the segmented viscoelastic bushing.

FIG. 2 illustrates a cross section of the segmented viscoelastic bushing.

FIG. 3 illustrates a perspective view of the viscoelastic bushing and the roller bearing hub.

FIG. 4 illustrates a perspective view of the viscoelastic bushing housed in the hub cavity.

FIG. 5 illustrates an exploded cross section of the segmented viscoelastic bushing housed in the hub cavity.

FIG. 6 illustrates a transverse cross section of a bushing embodiment.

FIG. 7 a illustrates a transverse cross section of another bushing embodiment.

FIG. 7 b illustrates a perspective view of another bushing embodiment.

DETAILED DESCRIPTION OF FIGURES

According to FIGS. 1 to 3, the present invention discloses a bushing which body (1), in annular shape, delimiting an inner groove (2) and an outer groove (3), designed with the purpose of absorbing the axial expansion variations during the electrical machine operation. The inner groove (3) delimits an inner ring (4), aiming join the segments (8) such that to facilitate its manipulation, making the bushing a single component.

The ring (4) presents in its perimeter one or more cuttings (6), in chute shape or other format, designed with the function of eliminating possible air accumulations during the assembly in the cavity bottom (11), in high and low relief, arranged such that to link the groove (3) inside the ring (4). The outer ring (7) presents segments (8) designed equidistant to each other and linked externally related to the perimeter of (7). Each projection (8) has a lower end (5) linked to the outer ring (7) and a beveled upper end (9), forming a rectangular trapezoid.

Also considering FIGS. 1 and 2, in a preferred embodiment, the inner groove (3) delimits an inner ring (4), presenting in its perimeter cuttings (6) in bas-relief, in chute shape, arranged such that to link the groove (3) to the ring inner side (4). In this construction, the outer ring (7) presents about eight segments (8) linked externally to the perimeter of (7). Each projection (8) has a curved end (5), and a beveled end (9).

According to FIGS. 3 to 5, the bushing (1) is fitted between the bearing and the wheel hub, such that to limit the axial and radial movement of the bearing (not shown) resulting from the existing clearance between the bearing and the bearing outer ring, limited to 20% of the air gap. The segments (8) of the viscoelastic bushing accommodate in rectangular cuttings (10) or also with identical format to the projections (8) and equidistant to each other, between the cavity (11) of the hub and the bearing.

The set axis-bearing can also offset axially in this configuration towards the hub wall. The inner ring (4) will replace the spring type washer wavy in spring steel, commonly used in conventional motors, compensating possible assembly axial mistakes, expansions and checking an axial pressure value needed for the bearing good operation.

According to FIG. 6, in another embodiment, the segments (13) are joined to a cross-section ring (16) in a T shape, joined through rectangular trapezoids grooved recesses (15). Each segment (13) presents a beveled upper end (14), and the lower end (12) with rounded corners.

In another embodiment, according to FIGS. 7 a and 7 b, the segments (20) present lower ends (19) curved and linked to the cross section ring perimeter (17), through the circular recessed grooves (18).

Certainly, it will be noted that other modifications and variations made to this invention are considered within the scope of this invention. 

1. Segmented Viscoelastic Bushing for Rotating Electrical Machines Bearing, to be used with the purpose of absorbing radial and axial expansion variations plus the mistakes generated by the high-pressure casting processes, during the electrical machine operation, comprising a body (1) in annular shape, delimiting an outer ring (7), presenting at least three segments (8) linked to the outer perimeter of (7).
 2. The Segmented Viscoelastic Bushing for Rotating Electrical Machines Bearing according to claim 1, wherein comprises an inner groove (2), an outer groove (3) and an inner ring (4) delimited by an inner groove (2) and outer groove (3), in order to link (2) and (3) to the ring (7); said inner ring (4) presenting cuttings in its perimeter (6).
 3. The Segmented Viscoelastic Bushing for Rotating Electrical Machines Bearing according to claim 1, wherein each segment (8) comprises a lower end (5) linked to the outer ring (7) and an upper end (9) in a trapezoidal rectangular shape or a rounding radius.
 4. The Segmented Viscoelastic Bushing for Rotating Electrical Machines Bearing according to claim 1, wherein in another embodiment comprises segments (13) joined to a cross-section ring (16) in a T shape through rectangular trapezoids grooved recesses (15); wherein each segment (13) presents a beveled upper end (14) and a lower end (12) with rounded corners.
 5. The Segmented Viscoelastic Bushing for Rotating Electrical Machines Bearing according to claim 1, wherein in another embodiment the segments (20) with curved lower ends (19) are linked to the ring perimeter of the rectangular cross-section (17), through circular recessed grooves (18).
 6. The Segmented Viscoelastic Bushing for Rotating Electrical Machines Bearing according to claim 1, wherein the segments (8), (13) and (20) of the viscoelastic bushing is housed in concave-shaped cuts (10) and equidistant to each other, between the cavity (11) of the hub and the bearing.
 7. The Segmented Viscoelastic Bushing for Rotating Electrical Machines Bearing according to claim 2, wherein each segment (8) comprises a lower end (5) linked to the outer ring (7) and an upper end (9) in a trapezoidal rectangular shape or a rounding radius.
 8. The Segmented Viscoelastic Bushing for Rotating Electrical Machines Bearing according to claim 2, wherein the segments (8), (13) and (20) of the viscoelastic bushing is housed in concave-shaped cuts (10) and equidistant to each other, between the cavity (11) of the hub and the bearing.
 9. The Segmented Viscoelastic Bushing for Rotating Electrical Machines Bearing according to claim 3, wherein the segments (8), (13) and (20) of the viscoelastic bushing is housed in concave-shaped cuts (10) and equidistant to each other, between the cavity (11) of the hub and the bearing.
 10. The Segmented Viscoelastic Bushing for Rotating Electrical Machines Bearing according to claim 4, wherein the segments (8), (13) and (20) of the viscoelastic bushing is housed in concave-shaped cuts (10) and equidistant to each other, between the cavity (11) of the hub and the bearing.
 11. The Segmented Viscoelastic Bushing for Rotating Electrical Machines Bearing according to claim 5, wherein the segments (8), (13) and (20) of the viscoelastic bushing is housed in concave-shaped cuts (10) and equidistant to each other, between the cavity (11) of the hub and the bearing. 